Gas-fueled infrared heaters for the purposes described are generally operated with natural gas or liquified gases and utilize temperature-resistant radiating elements in the form of wire fabric or mesh, perforated plates, perforated thermal bodies or the like. Surface temperatures with such irradiators are generally above 500.degree. C. and usually about 900.degree. C.
With such radiating heaters, a portion of the radiant energy is directly emitted from the radiating element onto the surface to be irradiated. Another portion of the radiant energy is reflected onto the surface as secondary radiation from the heater housing which can be formed as a reflector. The remainder of the radiant energy is lost from the outer surfaces of the housing. The efficiency of such an infrared heater can be about 50% and as a consequence can be too low for use in modern heating systems.
In infrared heaters of the aforedescribed type, the air supplied to the burner can be passed through a filter element which is located upstream of a mixing chamber in which combustion is effected or the fuel gas is admixed with the air supplied through the duct to sustain combustion.
In the applications described for such infrared heaters, for example, in construction and as animal-brooder heaters, such filters are essential since the ambient air often contains high proportions of dust.
Furthermore, in animal brooder installations, the ambient air which is drawn in to the heater may also have high moisture content. Both the dust and moisture content of the inducted air can lead to rapid reduction of the flow cross section of any filter element provided upstream of the burner nozzles and chamber to prevent contamination of the personnel.
Because of the reduction in the free cross section of the filter element, the ratio between the air and gas feeds to the burner can change from the stoichiometric.
The result can be an emission of carbon monoxide. The emission of carbon monoxide is, of course, dangerous because in many applications of such burners, the region in which the burner is used has limited fresh air access and the carbon monoxide can be detrimental to the health of personnel and animals in the region, even leading to death.
Since cleaning or replacement of filter elements, for example, during the brooder period of animals, is difficult to carry out because in part the heating should not be interrupted and the animals disturbed, earlier systems utilizing filters have not proved to be fully satisfactory. Furthermore, systems which require frequent replacement or cleaning of filter elements are also associated with high maintenance costs.